The present invention relates generally to a device system for generating a reversible working stroke and more specifically to such a system wherein the force varies during the working stroke. Objects of the present invention are also application devices for disk brakes which are controlled by the force generating device according to the invention.
Force generating systems of the above-mentioned type are provided for generating a reversible working stroke which acts in a defined direction and whose force is to be variable for a corresponding apportioning of the delivered output. In the invention, the working stroke generated by the force generating system acts upon a force take-up system of the type which, because of an essentially linearly increasing or decreasing elastic deformation, develops a counterforce which changes as a function of the stroke. Typical force take-up systems of this type are, for example, application devices for disk brakes, wherein the force which occurs when the brake shoes are pressed against the brake disk. Because of the limited rigidity of the application system, the force is converted to a corresponding elastic deformation of this system which exercises a corresponding counterforce on the force generating system. Although the force generating system according to the invention is intended particularly for use in application systems of this type for disk brakes, it can also be used in other force take-up systems which, when acted upon by force, develop counterforces in a comparable manner.
Particularly in the preferred field of usage of the invention, specifically with respect to application systems for disk brakes, a number of force generating systems are known for the application of the braking force. In the case of application systems provided for rail vehicles, the application force is generated, for example, by compressed-air cylinders whose compressed air, as a rule, is generated by the locomotive. The compressed-air cylinder, whose construction is known and therefore does not have to be explained any further at this point, when acted upon by compressed air, supplies its force by a brake clamp to the respective disk brake. This brake clamp has two clamp levers. On the brake-disk-side end of the brake levers, one brake shoe respectively is disposed which acts upon the brake disk. The brake levers are connected with one another in an articulated manner on a center connection element as well as on a connection element on the other end which faces away from the brake disk. At least one of the two connecting elements can be changed in its length for the application of the clamp levers and for the purpose of braking is adjusted by the driving rod of the compressed-air cylinder in such a manner that the brake clamp is applied. Concerning details about the construction of a brake clamp of this type and its operation, reference is made, for example, to German Patent Documents DE-PS 1 249 606 or DE-GM 17 04 651.
An alternative application system also used with disk brakes for road vehicles, among others, makes use of a so-called floating caliper which is disposed in a slidable manner in parallel to the axis of rotation of the disk brake. On one side of the disk brake, the caliper has a pressure-actuated, air-actuated or hydraulically actuated force generating device which presses, possibly by a mechanical power transmission, the brake shoe situated on this side against the disk brake. Whereupon, the caliper is displaced and, as a result, also presses the opposite brake shoe against the disk brake.
A disadvantage of the known force generating systems for application arrangements of this type is that, for the application and release of the brake (if the respective application device is operated in a so-called "fail-safe" arrangement, in the case of which an application takes place when the pressure medium is removed or fails), a comparatively large amount of energy has to be applied. This is the result of the relatively large required working stroke. Also, an application arrangement of this type is a system which deforms elastically when acted upon by pressure and which acts against the force generating device with a counterforce which increases as a function of the working stroke or the brake load and whose overcoming requires a large amount of energy. It is obvious that this high energy requirement should not be neglected, particularly in the case of trains with a large number of cars.
Another disadvantage of the known force generating system in the form of compressed-air cylinders or hydraulic cylinders is that the respective supplied force can be controlled only via the working pressure of the pressure medium which is comparatively difficult. Thus, for example, in the brake systems of rail vehicles, a sensitively apportioned braking operation can hardly be implemented.
It is an object of the invention to provide a force generating system for a force take-up system which is distinguished by a very low energy requirement and by a good apportioning capacity of the respective supplied force.
This object is achieved by the present invention.
The invention is based on the idea of minimizing the energy required by a force generator for the essentially linearly rising elastic deformation force take-up system, which produces a counterforce which changes as a function of the stroke. Also, during the reversal of the working stroke, the relaxation of the force take-up system, "charges" the energy-storing force generator used for generating the working stroke so that a correspondingly large portion of the energy applied during the force output is recovered. The invention therefore provides a type of "energy swing" between the two conditions "energy in the force generator" and "energy in the force take-up system", whereby finally a very high efficiency can be achieved. Because the energy-storing force-generating device acts upon the force take-up system via a force-transmitting lever mechanism, it is also achieved that the delivered force can be apportioned in an excellent manner.
As far as details are concerned, the operating principle of the force generating system is implemented by a lever mechanism including a pivot point fixed with respect to the force take-up system and including a lever arm for interconnecting with the force take-up system, of a given lever arm length. The energy-storing force generator acts upon the lever mechanism at a variable position of its lever arm. An adjusting arrangement controllably changes the position at which the force generator acts upon the lever arm of the lever mechanism. Tests have indicated that the energy to be applied by the adjusting device is in fact significantly lower than in the case of conventional force generating systems, such as compressed-air cylinders and the like.
The force generating device is preferably dimensioned such that the least amount of energy which is taken up by the respective force take-up system in the case of the maximal stroke or the largest lever arm length can be stored in it. In this manner, as little energy as possible is lost so that the efficiency can be optimized correspondingly.
A spring-loaded arrangement may be used, for example, as the energy storing force generator. This type of a spring-loaded arrangement is to be considered as a standard component so that the manufacturing will not be difficult. Optionally, as an alternative, a compressed-air-loaded arrangement or the like may also be used.
Preferably, the force generating device is arranged such that it is disposed in a swivellable manner with respect to the lever mechanism in a stationary bearing such that it rests against a lever arm surface of the lever mechanism in a swivellable manner. With respect to the bearing of the force generating device, this lever arm surface is constructed to essentially have the shape of a circular arc. This arrangement has the advantage that the adjusting arrangement of the force generating device, which is required for changing the working stroke of the force generating device, only needs to carry out a swivel movement which can be implemented in a simple manner.
Therefore, depending on the field of application of the force generating device, many different embodiments may be used for the adjusting arrangement. For example, it is possible to provide an electric adjusting motor which is coupled with the force generating device in a suitable manner. The coupling to the force generating device may be carried out in that, for example, an eccentric driven by the motor rests with its eccentric surface against a corresponding supporting surface of the force generating device. Depending on the angle of rotation of the motor shaft, a different swivelling angle of the force generating device is achieved. However, as an alternative, it is also possible to swivel the force generating device in a suitable manner by a connecting-rod driving device.
Furthermore, there is the possibility of generating the control force required for the adjusting arrangement by a compressed-air cylinder so that a pneumatic force generating device can be provided. From a control-technological point of view, the pneumatic force generating device hardly differs from a conventional pneumatic force generating device. The significant difference is the clearly lower energy consumption and the better apportioning capacity of the supplied force.
Another aspect of the invention, which is to be considered important, is that the lever arm surface of the lever mechanism may be designed such that the force which the force generating device requires for enlarging the working stroke is smaller than zero. In this manner, when the adjusting arrangement fails because of an absence of compressed air or electricity, as a result of this "gradient" of the lever arm surface, an automatic enlargement of the working stroke is achieved. When the present invention is used in disk brake application devices, the automatic enlargement can be utilized for carrying out an automatic braking operation ("fail-safe function").
As an alternative, it is naturally also possible to provide on the lever arm surface a reversed "gradient" in the direction of the reduction of the working stroke so that when the control force of the adjusting arrangement fails, the "0" working stroke of the force generating device is automatically obtained. In braking systems, this type of a function is used in practice particularly in the case of tunnel vehicles where it must be ensured that, if a braking device fails, the tunnel can be left at any time.
Furthermore, the gradient of the lever arm surface according to the invention has the advantage that the desired emergency position of the working stroke is achieved automatically when the mechanical coupling of the adjusting arrangement to the force generating device fails, for example, because of breakage of the mechanical coupling member.
Also, according to the invention, it may be possible to change the curved contour of the lever arm surface such that, despite the elastic extension of all force transmitting parts, only a minimal stroke of the force generating device is required. In this manner, it may be possible to further improve the energy balance.
It is recommended to select the respective swivelling angle range of the force generating device such that the force generating device, in the position which corresponds to the "0" working stroke, rests against a position of the lever arm surface of the lever mechanism in which the lever arm length is smaller than or equal to zero with respect to the working stroke direction. Irrespective of the respective selected gradient of the lever arm surface, a defined initial position is achieved by this "parking position" of the force generating device,
According to a further development of the invention, it is recommended to couple the force generating device by a correspondingly designed sliding element, with the lever arm surface in a displaceable manner. A roller may be provided for this purpose which is disposed on the lever-side end of the force generating device.
In order to prevent the lever arm of the lever mechanism from swivelling beyond the respective desired end positions, it is preferred that the lever arm rests against correspondingly placed stationary stops.
The force application point by which the lever mechanism acts upon the force take-up system may be provided on the lever arm of the lever mechanism as well as on an additional eccentric constructed on the lever mechanism. This force transmission from this application point to a pressure or tension rod may take place, for example, by a joint or the like.
In the simplest case, the lever bearing of the lever mechanism may be constructed as a bushing, although optionally sliding bearings or roller bearings may also be used for this purpose. According to the further development of the invention, it is advantageous in some applications to construct the lever bearing as a half-shell bearing. In this case, the force generating device, which is supported on the lever arm surface, clamps the lever mechanism in on the side opposite the half-shell bearing and therefore prevents the lever mechanism from falling out of the half-shell bearing.
A further aspect of the invention which is considered significant is that the force generated by the force generating system, in contrast to conventional devices, can be measured in a extremely simple manner in that the momentary swivelling angle of the force generating device is detected and/or in that the momentary working stroke is measured. The swivally angle can be sensed by a sensor which senses either the position in which the force generating device acts upon the lever arm of the lever mechanism or which senses the momentary swivelling angle of the force generating device. The momentary working stroke may be sensed by a sensor which detects the momentary working stroke either directly or by way of the momentary angular position of the lever arm of the lever mechanism.
When the force generating system according to the invention is used as an application device of a disk brake, it is recommended that both above-mentioned force detecting variants be provided to determine a possible wear of the lining of the brake shoes from a difference of the two output signals of the sensors. Specifically, if a wear of the brake shoes has occurred, the brake shoes will rest against the brake disk at a later point in time or at a different angular position of the lever arm so that so that the elastic deformation of the application device, which is reflected by the working stroke, occurs at a correspondingly later point in time. The difference signal of the two sensors can therefore be used for the control of an adjusting device.
When the force generating system according to the invention is used for an application device comprising a floating caliper, it is recommended to couple the end of the rod of the force generating device to the force application point to act against the brake shoe disposed in the floating caliper. In this manner, a particularly simple construction of the application device is achieved.
However, when the force generating system according to the invention is used for an application device which comprises a braking clamp, as an alternative, the force generating system may form either the center connection element of the two clamp levers or the end connection element which faces away from the brake disk. In this case, the respective other connection element of the two clamp levers is preferably formed by a wear adjusting device. A particularly space-saving arrangement which is easy to produce can be achieved in this case when the swivellable force generating device is disposed coaxially with respect to one of the two pivot bearings of the center or end connection element of the corresponding clamp lever of the brake clamp. Optionally, in this manner a single bolt may be sufficient for the bearing of the clamp lever and of the force generating device. However, in the case of this bearing variant of the force generating device, it should be endeavored to arrange its axis with respect to the lever arm element of the lever mechanism in such a manner that no buckling moment can be exercised on it.
When the invention is used for one of the disk-brake application devices, it is generally possible to shape the lever arm surface of the lever mechanism advantageously in such a manner that the application stroke for overcoming the venting play can be carried out by a slight swivel movement of the force generating device. That is, the lever arm surface has, for example, a progressively "decreasing" slope in the application direction. As a result, it is possible to carry out the application stroke very rapidly so that a correspondingly larger variation range of the respective generated force is available for the braking operation.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.